Equalizers of this type are well known per se and usually include a number of weighting networks to which corrective voltages are applied, the magnitude of these voltages being selected in accordance with the amplitude and phase responses of the channel. In a transversal equalizer, the several weighting networks have input connections to respective taps of a delay line and output connections to a component such as a summing amplifier delivering a combination of all the processed signals, tapped off the delay line, to a load.
Conventional weighting networks, serving to multiply the amplitudes of the variously delayed signals by selected analog coefficients under the control of the corrective voltages applied thereto, include amplifiers of the automatic-gain-control type which, however, require rather complex circuitry especially with signals of large bandwidths. If field-effect transistors are used as the active elements of the networks, serious limitations are imposed upon the maximum amplitudes of the signals to be processed.
One of the problems to be solved in such a transversal equalizer is the undesirable cross-coupling among the several weighting networks resulting from the changes in the effective network impedances, due to the applied corrective voltage, which affect the signals tapped off at other points of the delay line. Another problem is that of effectively measuring the impedance changes induced by the corrective voltage in order to stabilize the weighting coefficient selected for each network.